A wide variety of air and water barrier systems are used in both new building and remedial construction applications. These barrier systems are designed to eliminate uncontrolled air and water leakage through e.g. exterior walls and/or facades enabling the control of e.g. temperature, humidity levels, moisture levels and air quality throughout a building thereby minimising, for example, the possibility of damp problems and/or the chance of mould growth and poor air quality.
Air barriers are designed to minimise and potentially exclude the passage of air through, e.g., walls. Water barriers are intended to minimise or exclude the ingress of liquid water from entering a building through a wall or façade or the like e.g. via capillary action through cracks, holes or porous materials. The application of such barrier systems to constructions, e.g. cavity wall systems, results in energy cost savings and may significantly reduce the ingress of airborne pollutants by substantially reducing the amount of air leakage through the exterior walls or facades of a building.
A single material can function as an air and water barrier. Air and water barriers are typically found in two forms, sheet materials and liquid coating compositions. Each type is usually designed to be either (water) vapour permeable or impermeable. Vapour Impermeable Air and water barrier coatings effectively block the transfer of water vapour through the coating, whilst vapour permeable Air and water barrier coatings control the amount of (water) vapour diffusing through a wall due to variable vapour pressures. Unless prevented or controlled, water vapour will naturally move from a high concentration to a lower concentration until it is in balance. Hence, if the vapour pressure is high outside the wall and low inside the wall, vapour will be directed inward (and vice versa).
The use of liquid-applied vapour permeable air and water barriers for wall assemblies has only recently significantly increased, not least because air leakage has become recognized as a potential source of moisture accumulation in walls. This type of air and water barrier is designed to allow moisture vapour to pass through the membrane, promoting diffusion. Determining whether to use a vapour permeable or vapour impermeable air and water barrier (and indeed the degree of vapour permeability in a selected barrier) is determined through local climate of the building and the wall design itself i.e. the inter-relationship of the air/water barrier and the insulation layer are located in relation to each other in the wall.
Liquid-applied Vapour permeable, air and water barrier coatings can be formed by applying a liquid coating composition onto a suitable internal building construction surface. Liquid-applied air and water barriers are rolled, sprayed or trowelled onto substrates and become part of the internal structural wall. Because of the way they are applied, there are no fastener holes from the installation where water penetration may occur, and there is no potential for mislapping or tearing, as with many sheet materials.
Another important distinction of a liquid-applied air and water barrier in wall assemblies is that they can minimize application error and unintentional air infiltration caused by the over-lapping of sheet applied materials. The liquid-applied materials are applied and dry or cure as a monolithic membrane around the building envelope.
A variety of both vapour permeable and impermeable air and water barrier coatings are commercially available with the vast majority being organic based coatings. Unfortunately however, these organic based coatings have compatibility issues with silicone based materials, such as caulks and weather sealants. The lack of compatibility may lead to the inability to use such silicone materials or the need for complex and potentially additional layers of adhesives, primers and/or adhesion promoters prior to application of silicone caulks and/or sealants etc. This renders the construction process more expensive and complicated as it may necessitate additional labour and more complicated application processes in order to provide a “weather-tight” building.
Another disadvantage with organic coatings of the type currently used for currently typically used is that they have poor UV stability (unlike silicone based materials) and as such cannot be exposed to UV radiation for extended periods of time during construction without necessitating re-application of one or more additional coating layer(s), which obviously adds to the cost of the process. WO2012/064611 proposes a silicone based fluid applied silicone air and water barrier system.